1. Field of the Invention
The present invention relates to an inverted pendulum type vehicle. More particularly, to an inverted pendulum type vehicle provided with a sub-wheel for facilitating turning (turning-round) in addition to a main wheel.
2. Description of Background Art
An inverted pendulum type vehicle is known wherein the inverted pendulum type vehicle includes a vehicle body frame, a main wheel having a plurality of rotatable driven rollers combined so that axes of rotation of the driven rollers are in an annular form with left and right driving disks rotatably supported on the vehicle body frame so as to be located respectively on both sides of the main wheel and substantially coaxially with the axis of rotation of the main wheel. Each of the driving disks is provided with a plurality of rotatable driving rollers disposed so as to make contact with the driven rollers in a twisted relationship. Driving means is provided for individually driving the left and right driving disks. See, for example, Japanese Patent Laid-Open No. 2011-63243.
The inverted pendulum type vehicle according to Japanese Patent Laid-Open No. 2011-63243 can move forward and rearward by rotating the left and right driving disks and rotating the main wheel around an axis that extends in the left-right direction. In addition, the inverted pendulum type vehicle can move leftward and rightward by rotating the left and right driving disks with a speed difference therebetween and rotating the driven rollers. In this way, the inverted pendulum type vehicle can travel in any of a forward, rearward, leftward and rightward directions.
The inverted pendulum type vehicle according to Japanese Patent Laid-Open No. 2011-63243, however, has a difficult problem with respect to a leftward and a rightward turning (turning-round), through it is good at forward, rearward, leftward and rightward movements. One of considerable solutions to this problem is to provide a sub-wheel in addition to the main wheel and to turn (turn round) the inverted pendulum type vehicle by utilizing a frictional force generated between the sub-wheel and a floor surface or a driving force generated by the sub-wheel. In regard to such an inverted pendulum type vehicle, a configuration can be contemplated in which the sub-wheel is supported by a sub-wheel arm provided to be turnable in the vertical direction relative to the vehicle body frame with the sub-wheel being grounded under its own weight. However, when it is assumed that some external force for pressing the sub-wheel arm down is exerted on the sub-wheel arm, the sub-wheel is enlarged more than necessary, for the purpose of securing a load resistance of a rotary shaft of the sub-wheel or a support structure for the rotary shaft.